(a) Field of the Invention
The present invention relates to an orthogonal frequency division multiplex (hereinafter, referred to as “OFDM”) system. More specifically, the present invention relates to a transmitting and receiving method for reducing a distortion caused by a time-varying channel in a high-speed mobile environment.
(b) Description of the Related Art
The OFDM system involves insertion of a cyclic prefix (CP) longer than the impulse response of a channel in a guard interval between adjacent OFDM symbols to eliminate the interference between the symbols, and thereby allows compensation of a fading channel distortion simply by using a single tap equalizer at the receiver. The OFDM system also allows rapid realization of a modulation/demodulation process at the transceiver by using an inverse fast Fourier transformer (IFFT) and a fast Fourier transformer (FFT).
These advantages of the OFDM system enable development of high-speed data transmission systems, for example, OFDM wireless communication systems including digital audio broadcasting (DAB), digital video broadcasting (DVB), digital terrestrial television broadcasting (DTTB), wireless local area network (LAN), wireless asynchronous transfer mode (ATM) or the like. Recently, these OFDM wireless communication systems have been actively studied as a core technology of the fourth generation mobile communication.
To improve the link budget of wireless channels, various multi-antenna OFDM technologies such as SFBC(Space-Frequency Block Coded)-OFDM, SFTC(Space-Frequency Trellis Coded)-OFDM, MRRC(Maximal Ratio Receiver Combining)-OFDM and so forth have been studied. But the OFDM systems with multiple antennas have a distortion caused by a time-varying channel as the OFDM systems with a single antenna, and hardly guarantee a high diversity gain at high speed mobile environment with multiple antennas, thereby deteriorating the performance.
A conventional method for solving the problem involves transmission of pilot symbols to estimate a time-varying channel distortion and compensation of the estimated distortion. In this method, however, the pilot symbols have to be transmitted prior to data symbols, causing a high overhead and a deterioration of performance due to the use of an estimated channel before one symbol.